This invention relates generally to a pump valve for use in high pressure applications such as advanced controlled vehicle braking systems.
In conventional design of hydraulic modulators for controlled braking systems where brake self-apply is required, such as traction control, and vehicle stability enhancement systems, it is usual to incorporate a normally closed valve assembly between a main master cylinder port and an inlet of a recirculation pump. The valve functions to isolate flow from a master cylinder to the pump inlet when the pump is idle, and to provide a flow path to the pump inlet when the pump is running. Traditionally, a normally closed single poppet-type valve with a suitably designed poppet and seat is commonly employed for this function. This type of valve works well for all systems which permit valve actuation under very low braking pressures.
However, under high master cylinder pressures, the force requirements needed to open the single large poppet valve are high. These force requirements to open the valve are proportional to an area of a main control orifice valve seat of the valve assembly. In order to open the valve under high pressures an exceedingly large solenoid coil and a large amount of magnetic force as generated by an electrical current are required. In the newer type of controlled braking systems, such as vehicle stability enhancement, such high pressure requirements frequently occur. Failure of the valve to open during high pressure use is unacceptable. While the newer brake systems require operation under high pressures, traditional requirements such as operation during very low pressure, cold temperatures remain a requirement of the valve assembly.
Previous solutions to these requirements have utilized two separate valves, one for high pressure/low flow and one for low pressure/high flow situations. However, the two valve designs are more costly and require additional packaging space.
Thus, it is desired to design an efficient high flow pump valve which has the capability to function during all expected conditions including opening under high braking pressures.
The present invention is an efficient two-stage, two-poppet prime valve assembly. The valve assembly utilizes one valve and two poppets for allowing the valve assembly to open under high pressure while providing minimal internal flow restrictions to enhance cold temperature and low pressure operation. Such conditions are present in modern vehicle braking systems. The two-stage poppet design contains two separate flow paths, one being high pressure, relatively low flow comprising a stage one, and the other being relatively low pressure, high flow comprising a stage two. In addition, the valve incorporates a reverse flow bypass feature that is capable of checking flow at very high pressure yet allowing reverse flow with a very low pressure drop.
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the presently preferred embodiment. The drawings that accompany the detailed description can be described as follows: